Added CORS middleware. Updated umami script.

lib/middleware.js

@@ -0,0 +1,20 @@
+import cors from 'cors';
+
+export function use(middleware) {
+  return (req, res) =>
+    new Promise((resolve, reject) => {
+      middleware(req, res, result => {
+        if (result instanceof Error) {
+          return reject(result);
+        }
+        return resolve(result);
+      });
+    });
+}
+
+export const allowPost = use(
+  cors({
+    origin: '*',
+    methods: ['POST', 'OPTIONS'],
+  }),
+);